Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 4,494,914 discloses a fluid displacement apparatus which includes a pair of interfitting scroll members. Each scroll member has a circular end plate and a spiral element extends from one end surface of the end plate. These scroll members are maintained angularly and radially offset so that both spiral elements interfit and make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbit motion of the scroll members shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pocket changes. Since the volume of the fluid pockets increases or decreases according to the direction of the orbital motion, the scroll type displacement apparatus is applicable to compress, expand or pump fluids.
To achieve smoother operation of such scroll type displacement apparatus, the inner and outer wall surfaces of spiral element and the axial end surface of the end plate should be finished over their entire surfaces by a conventional turning process.
However, it takes a long time to finish by turning the entire surfaces of the scroll elements. Also, since the entire surface of the scrolls are finished by turning, a considerable amount of materials from the scrolls is wasted.